Hydraulic motors and pumps



United States Patent [72] inventors Donald Firth, Glasgow, Scotland Sinclair Cunningham, Glasgow, Scotland [21] AppLNo. 699,410 [22] Filed Jan. 22, 1968 [451 Patented Sept. 8, 1970 [731 Assignee National Research Development Corporation London, England a corporation of Great Britain 1 [32] Priority Jan. 27, 1967 [33] Great Britain [31] 4,240/67 [54] HYDRAULIC MOTORS AND PUMPS 6 Claims, 5 Drawing Figs.

[52] US. Cl. 91/498, 91/65, 60/53, 91/505, 91/472, 92/56, 417/315, 417/429 [51] Int. Cl F046 1/10, F01b 3/00, FOlb 13/04 [50] Field ofSearch 92/56, 57, 58,66,71.72; 103/1 IA, 161, 162, 161B; 60/538, 53; 91/175, 197, 198, 202

{56] References Cited UNITED STATES PATENTS 1,325,434 12/1919 Careyet a1 ..l03/l61(B)UX Primary Examiner+Martin P. Schwadron Assistant Examiner-Irwin C. Cohen Attorney-Larson and Taylor ABSTRACT: The combination of a hydraulic motor of the kind which comprises a cylinder block containing a number of pistons adapted to bear against a multi-lobed cam track so as to cause a torque to develop between the block and the cam track, the motor being arranged to drive an output shaft, with a second motor arranged to drive the same output shaft. and including means to disengage the first motor from the output shaft by lifting and holding all of the pistons of the first motor clear of the cam-track or by arresting movement of the pistons along the cam track.

IA 48 I43 456 47 5 A r 11 1 is 1 57 60 5 6/ 65 67 Patented Sept. 8, 1970 Sheet 0 h l I u mm @N v/////////////// Ah Q kw m mm ww 4% w MN Ill MI W a @Q 7 n v vhf/4W! I Q Q Q a 3 QM M V//////////V///////////V m\k\ WW Q 3 Patented Sept. 8, 1970 HYDRAULIC MOTORS AND PUMPS This invention relates to improvements in hydraulic pumps and motors, and has for its object the provision of a hydraulic pump or motor unit which is capable of accommodating a wider range of torque/speed requirements than existing hydraulic units.

According to the invention there is a hydraulic motor of the kind which comprises a cylinder block containing a number of pistons adapted to bear against a multi-lobed cam-track so as to cause a torque to develop between the block and the cam track, the motor being arranged to drive an output shaft in combination with a second motor arranged to drive the same output shaft, and including means to disengage the first motor from the output shaft by lifting and holding all of the pistons of the first motor clear of the cam-track or by arresting movement of the pistons along the cam-track.

According to one aspect of the present invention, a hydraulic unit motor includes a first hydraulic motor arranged to drive an output shaft, a second hydraulic motor also arranged to drive the output shaft, the first hydraulic motor including cylinders and pistons and a cam-track arranged to produce at least one reciprocation of each piston during each rotation of the motor, and the second hydraulic motor including cylinders and pistons and a cam-track arranged to produce a greater number of reciprocations of each piston during each rotation of the motor than does the cam-track of the first motor and control means arranged when actuated to ensure that the pistons of the second motor do not travel at high speed over the surface of their cam-track during driving of the output shaft at high speed by the first motor.

Thus the pistons of the second motor may be lifted away from their cam-track or their movement along their cam-track may be arrested.

One type of hydraulic motor in general use today is the ball motor in which a plurality of balls serving as pistons are disposed respectively in radially extending cylinders in a cylinder block and engaged at the radially outer ends of the cylinders a cam-track which is rotatable about the cylinder block. Such a motor will have say 16 cylinders and say four lobes in the cam-track, so that for each revolution of the cylinder block relative to the cam-track each cylinder has four working strokes, giving a total of 64 working strokes per revolution. This leads to a motor with a large through flow of hydraulic fluid, giving a large turning torque for a given size of motor, but in view of the large number of strokes performed by each piston per revolution ofthe cylinder block this type of motor is used at relatively low speeds of up to say 500 revolutions per minute.

Another type of hydraulic motor in general use today is the swashplate motor, in which a rotatable cylinder block is formed with say nine cylinders extending parallel to its axis of rotation and containing pistons which act through slipper pads on a flat plate (called a swashplate) inclined at an angle to the axis of rotation of the cylinder block. In such a motor each cylinder performs one working cycle for each revolution of the cylinder block. Thus when a motor is required to run at say 3,000 revolutions per minute, the swashplate motor is adopted in preference to the ball motor. Although a swashplate motor can be built to produce a large torque while working at relatively low rotational speed such a motor inevitably is much larger and heavier than a ball motor of equivalent output.

According to a second aspect of the present invention a hydraulic motor unit includes a housing, a hydraulic swashplate motor carried in or on that housing and arranged to drive an output shaft carried in or on that housing, a rotary radial piston motor, including a plurality of pistons engaging a camtrack, also carried in or on that housing and also arranged to drive the output shaft, and control means arranged when actuated to render the radial piston motor ineffective to drive the output shaft and to ensure that the radial pistons ofthat motor do not travel at high speed over the surface of the cam-track.

According to a third aspect of the present invention, a hydraulic motor unit includes a housing, a hydraulic swashplate motor carried in or on that housing and arranged to drive an output shaft carried in or on that housing, a rotary hydraulic radial piston motor also carried in or on that housing and including a plurality of radial pistons carried individually in radial cylinders, and effective to produce a torque by action against a suitable cam-track, the radial piston motor also being arranged to drive the output shaft, and control means arranged when actuated to hold the radial pistons inwardly away from the cam-track so that at high speeds of operation the swashplate motor can drive the output shaft but the radial pistons of the ball motor do not travel over the surface of the cam-track.

According to a fourth aspect of the present invention, a hydraulic motor unit includes a housing, a hydraulic swashplate motor carried in or on that housing and arranged to drive an output shaft carried in or on that housing, a rotary hydraulic radial piston motor also carried in or on that housing and including a plurality of radial pistons carried individually in cylinders, and effective to produce a torque by action against a suitable cam-track, the radial piston motor also being arranged to drive the output shaft, and control means arranged when actuated to hold the radial pistons firmly against the cam-track so as to preclude movement of the radial pistons along the track, so that at high speeds of operation the swashplate motor can drive the output shaft but the radial pistons of the ball motor do not travel over the surface of the cam'track.

The invention will now be particularly described, by way of example, with reference to the accompanying drawings, in which:

FIG. I is a sectional side elevation ofa hydraulic motor unit arranged to drive the chuck ofa lathe;

FIGv 2 is a diagrammatic representation of a hydraulic system including the motor unit of FIG. 1;

FIG. 3 is a graph indicating the performance of the hydrau lic motor unit shown in FIG. 1;

FIG. 4 is a sectional side elevation of an alternative form of hydraulic motor unit arranged to drive the chuck of a lathe; and

FIG. 5 is a cross-sectional view of a ball motor of the type used in the present invention,

Referring first to the embodiment of the invention shown in FIG. I, the hydraulic motor unit includes a housing 1 and a rotor 3 rotatably mounted in the housing and fixedly coupled to a chuck 5 arranged to rotate with the rotor and to accommodate a workpiece.

The housing 1 is generally cylindrical in shape, being built up from front end part 1A, a central cylindrical part 18, and a rear end part 1C, which are suitably bolted together. The rotor 3 comprises a generally cylindrical main part 3A having an enlarged front end part 38 to which is bolted a nose part 3C. Nose part 3C has a frusto'conical outer surface 11 which engages a complementary bearing surface 13 provided in the end part 1A, this bearing surface positioning this end of the rotor radially and also against forward movement, Lee. to the left in FIG. I, The enlarged front end part 38 of the rotor has a frusto-conical outer surface 15 which engages a complementary bearing surface 17 provided on an inwardly extending flange 19 on the central body part 18, this bearing surface assisting in the positioning of this end of the rotor radially and also positioning the rotor against rearward movement, [.e. to the right in FIG. 1. The rear end ofthe rotor includes a cylin drical part 21 which extends through and is radially positioned by a journal bearing 23 carried by the housing rear end part 1C. Extending centrally through the rotor 3 is a mechanism (not shown) for opening and closing the jaws of the chuck 5, this mechanism forming no part of the present invention.

The enlarged end part 38 of the rotor is formed with eight radially extending bores 41 forming the cylinders of a ball motor, these bores containing balls 43 which are pressed outwardly by hydraulic fluid contained in the radially inner parts of the bores against an annular cam-track 45. Cam-track has a profile, as viewed from the left in FIG. I, of valleys alternating with crests, the arrangement being such that the balls 43 can follow the profile, as the rotor is rotated relative to the housing 1, while remaining in their cylinders. A motor of this type, viewed from the left, would resemble FIG. 5, except that the latter shows nine radially extending bores 41 rather than eight. Hydraulic fluid under pressure is admitted to, and exhausted from, the inner ends of the cylinders through first and second ducts 46 and 47 (see FIG. 2) continued in the housing 1 as further ducts, formed in the enlarged end part 38 of the rotor, consecutively come into register with ports in the surface 17. Such ball motors are in themselves well known. An annular duct 48 extending between parts of the end part 1A and the central part 18 communicates with the annular space between. the cam-track 45 and the enlarged end part 3B of the rotor and with a third duct 49 extending into the housing and to whichhydraulic fluid under pressure can be admitted. The ar rangement is such that the rotor can be driven by the ball motor in one direction by the admission of fluid under pres sure to the first duct 46, while fluid is exhausted from the second duct 47 and the third duct 49 is at zero gauge pressure; it can be driven in the opposite direction by the admission of fluid under pressure to the second duct 47, while fluid is exhausted from the first duct 46 and the third duct 49 is at zero gauge pressure; and it can be rendered free to rotate without engagement of the balls 43 with the cam-track 45 by the admission of fluid under pressure to the third duct 49 while the first and second ducts 46,47 are maintained at a relatively low pressure, the oil pressure then forcing all the balls inwardly into their respective cylinders and away from the track.

The part of the rotor 3 between the enlarged end part 3A and the rear end is formed over part of its length with splines 51 and a cylinder block 53 of a swashplate hydraulic motor is formed with a complementary bore and is fitted on to this part of the rotor. Interposed between the front end of the cylinder block 53 and the rear face 55 of the flange 19 is a ported valve member 57, also formed with a central bore complementary to the splined part of the rotor, so that it rotates with that rotor. Fourth and fifth ducts 58, 59 formed in the housing central part 18 terminate in ducts in the rear face 55 of the flange 19. The cylinder block 53 is formed with nine cylinders 60 evenly spaced around, and with their axes parallel to, the axis of the rotor 3. Each cylinder contains a piston 61 acting at its outward end (to the right in FIG. 1) on a slipper pad 63 to which it is coupled by a balI-and-socket joint 65. The heads of the cylinders 60 (to the left in FIG. 1) are connected to ports in the valve member 57, and the arrangement is such that the port in a cylinder 60 is during about one half of the rotors rotation in communication with the fourth duct 58, and during substantially the whole of the remainder ofthe rotors rotation is in communication with the fifth duct 59. The slipper pads 63 bear on a swashplate 67 which is journalled for adjustment about the stub axles 69 carried by the housing 1. It will be appreciated that with the plate in the position shown, as hydraulic fluid is admitted under pressure to the fourth duct 58 and allowed to exhaust through the fifth duct 59, at any one time four or five of the nine pistons will be forced towards the right in FIG. 1, and that the reaction between the slipper pads of these pistons and the surface ofthe swashplate will cause rotation of the rotor relative to the fixed swashplate. On the other hand, if the swashplate is adjusted so that the rotor axis is normal to the plane of the surface engaged by the slipper pads, no such reaction force causing rotation will be set up. In practice, for a given throughput of hydraulic fluid, the speed at which the rotor is driven depends upon the angle to which the swashplate is set.

FIG. 2 illustrates how the hydraulic motor unit of FIG. 1 is incorporated in a hydraulic circuit. This circuit includes a swashplate hydraulic pump 81 driven by an electric motor 83 and having two hydraulic input-output pipes 85 and 89 connected to a unit 91. The ducts 46, 47 and 49 are all connected to this valve unit, and the valve unit can be set to supply hydraulic fluid to, and exhaust that hydraulic fluid from, these different ducts as mentioned above. The electric motor 83 is a constant speed motor, and the flow rate of hydraulic fluid is determined by the setting of the swashplate 93 of that pump. The pressure in the hydraulic fluid will depend upon the load exerted on the system by the hydraulic pump unit.

In use of the hydraulic motor unit shown in FIG. 1 and described above, the rotor can be driven either by the ball motor or by the swashplate motor as desired. Thus if hydraulic fluid is supplied under pressure to the first duct 46, the second duct 47 being connected to exhaust and the third duct 49 being connected to a drain, then the ball motor will be effective to turn the rotor. When the motor is to be driven as a swashplate motor, the first and second ducts 46, 47 are connected to exhaust and the third duct 49 is connected to a source of hydraulic fluid under pressure. The hydraulic fluid from the third duct 49 flows into the annular duct 48 and into the space within the cam-track 45 and serves to force the balls 43 inwardly out of engagement with the track. At the same time, the swashplate 67 is inclined to the axis of the rotor at an angle which is determined by the speed at which the rotor is to be driven, and hydraulic fluid admitted to the fourth duct 58 under pressure and exhausted from the fifth duct 59. As described above, this causes rotation of the rotor by reaction between the slipper pads 63 and the swashplate 67.

The advantage of the hydraulic motor units described above is that for a constant power input from the hydraulic pump 81 the motor unit can supply a very large torque at a low speed of turning of the rotor 3, or a small torque at a high speed of turning of the rotor 3, and yet its overall size and its weight are, compared with previous hydraulic motors of comparable output, small. This can be seen from a consideration of the operating characteristics of ball and swashplate motors. A ball motor can produce a very large torque and yet can be small in size and light in weight. However, the speed at which a ball motor can run is limited by the stresses on the cam, and the practical limit at the time of writing is about 500 revolutions per minute for motors having mean diameters for their camtracks of say seven inches to one foot. On the other hand, a swashplate motor can readily run at speeds of say 3,000 r.p.m., but such a motor must be large and heavy if it is to produce a large torque.

These facts are illustrated by the graph in FIG. 3, curve A of which shows for the present hydraulic motor unit the correlation of speed and torque when the motor unit is supplied with hydraulic fluid at a pressure and at a throughflow rate to which the speed range I50 r.p.m. to 3,000 r.p.m. corresponds at all times to a power input of 30 brake horse-power. The maximum available pressure prevented this power input being maintained for speeds under r.p.m. Over the speed range from zero to 416 r.p.m. the ball motor is effective, its speed being controlled by its fluid throughput, i.e. by setting of swashplate 93 of the pump, and the torque at first remains constant over the speed range zero to 150 r.p.m., being determined completely by the maximum available hydraulic fluid pressure, i.e. about 3,000 pounds per square inch. At l50 r.p.m. this maximum available pressure produced a power input of 30 brake horse-power, and from then onwards as the speed was increased the limiting factor was the power input, held constant at 30 brake horse-power. The torque produced by the ball motor fell progressively from 12,500 lbs. f. ins. to about 500 lbs. f. ins. and the oil pressure also fell as indicated by curve B. Above the speed of 416 r.p.m., the ball motor is running at an excessive speed, and therefore as described above the mode of operation is modified by rendering the ball motor ineffective and bringing the swashplate motor into operation. The maximum torque called for from the swashplate motor is only 500 lbs. f. ins., and the size and weight of this motor and much less than would have been the case had a maximum torque of 12,500 lbs. f. ins. been required. Curve B indicates how the working pressure of the hydraulic fluid varies during operation according to curve A.

Referring now to the embodiment of the invention shown in FIG. 4, this hydraulic motor unit includes a housing 1 and a rotor 3 rotatably mounted in the housing and fixedly coupled to a chuck 5 arranged to rotate with the rotor and to accommodate a workpiece. The main difference between the embodiments of FIGS. 1 and 4 is that in the embodiment of FIG. 4 a rotary shaft 401 is also rotatably mounted in the housing and is coupled to the rotor 3 by a gear wheel 403 fixed on the shaft and engaging a gear wheel 40S fixedly mounted on the rotor 3, a swashplate motor 409 having its cylinder block 411 mounted on the shaft 401 and a ball motor 413 being mounted on the rotor 3. Items in FIG. 4 which correspond to parts shown in FIG. I and described above are indicated by the reference numerals used for corresponding parts in FIG. 1.

The manner of operation of the hydraulic motor unit shown in FIG. 4 is substantially the same as that of the unit shown in FIG. I, the balls of the ball motor being held off their track 45 when it is desired to run the chuck at high speed by the swash plate motor.

The invention can also be applied to the driving ofa hydraulic pump unit where the power input is to a shaft the driven speed of which and the available torque on which vary in use over a wide range. In such an arrangement, it could be advantageous to use a *pump equivalent of a ball motor in conjunction with a pump" equivalent ofa swashplate motor.

We claim:

l. A rotary hydraulic assembly comprising a first rotary hydraulic device and a second rotary hydraulic device; the first device having two elements namely a first cylinder block and an multi-lobe cam track, said first block having spacedapart cylinders each containing a piston, the first block and the cam traclt being mounted for relative motion with the pistons engaging the lobes of the cam track in succession; a space between the pistons and cam track of the first device isolated from the second device; the second device having two elements namely a second cylinder block and a camming means, said second device having spaced-apart cylinders each containing a piston, the said second block and camming means being mounted for relative motion with the pistons engaging the camming means; a mechanical connection between one of the elements of each device, the other element of the two devices being anchored to fixed parts of the assembly, said camming means of said first device being constructed so that each piston of the first device makes substantially more strokes to and fro along its cylinder than does each piston of the second device, for a given motion of the two elements mechanically coupled together as aforesaid; means connecting a high pressure region to the cylinders of said first and second devices; first valve means controlling the flow of fluid under pressure between the high pressure region and the cylinders of the first device in succession according to their progress along the lobes of the cam track, second valve means for cutting off the cylinders of the first device from the high pressure region and exhausting them to a low pressure region, and means for maintaining said space between the pistons of the first device and the cam track filled with fluid at a pressure slightly in excess of the pressure in the said low pressure region whereby, on operation of the second valve means, the pistons of the first device are forced out of engagement with the cam track and the second device alone is operable.

2. A rotary hydraulic assembly according to claim 1 with coupling means for connecting the said two elements mechanically coupled together to a prime mover, whereby the said assembly is driven and acts as a pump.

3. A rotary hydraulic assembly according to claim 1 and in which the second device is a swashplate hydraulic device.

4. A rotary hydraulic assembly according to claim I and in which the pistons of the first device are in the form of balls.

5. A rotary hydraulic assembly according to claim 1 and in which the first device has its pistons arranged radially.

6. A rotary hydraulic assembly according to claim 1 and in which the first and second devices are contained in a common casing. 

